Different interests between mating partners regarding the fate of their gametes can lead to sexual conflicts in many species. Although these conflicts can sometimes be dealt with pre-copulatorily (e.g. by choosing with which partners to mate), they often extend beyond copulation. Post-copulatory sexual conflicts are expected to be particularly strong in simultaneous hermaphrodites because an individual may have to accept sperm in order to obtain an opportunity to donate sperm, reducing the effectiveness of pre-copulatory conflict resolution. The present study investigates the post-copulatory interactions between male and female sexual traits of a highly promiscuous simultaneous hermaphrodite, the free-living flatworm Macrostomum lignano. Using light and electron microscopy, we show the different levels of complexity of the sperm and the genitalia, and derive hypotheses about how the different traits may represent evolutionary responses to such sexual conflicts.

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Abstract. Two mouthless interstitial animals, a nematode and a turbellarian were collected from reduced sediments surrounding polychaete tubes. The microorganisms in the gut rudiment of the two animals were described using TEM. The occurrence of mouthless freeliving marine animals in relation to organic and sulfide rich environments and their association with microorganisms is discussed. A description of Astomonema jenneri n.gen., n. sp. (Nematoda, Siphonolaimidae) is given in an appendix.

Rieger, R. M. the fine structure of gastrotrichs u'ith description of Chordodasys antennatus sp.n. 2001. Scr. 3 (5-6): [219][220][221][222][223][224][225][226][227][228][229][230][231][232][233][234][235][236][237] 1974.-Chordodasys antennatus sp.n. is described from sublittoral sediments off the US Atlantic Coast. This species has been also studied by transmission electron microscopy. The new species is particularly characterized by extremely enlarged sensory processes which have a segmented appearance. The fine-structure of the chordoid organ, characteristic of the genus Chordodasys, has been studied in both known species of this genus. According to this investigation the chordoid organ consists of plate-like muscle cells, surprisingly similar to the notochord of Amphioxus. Particular emphasis has been made in this study to elucidate the fine structure of the body cavity and the system of lateral and central chambers as described by Remane in 1936. The electron micrographs substantiate the fact that gastrotrichs exhibit an acoelomate construction of their body cavity. The systematic position of the new species and the genus Chordudusys is discussed in the light of the new ultrastructural information. Occurrence Specimen IS I was collected a t 97 m depth in sandy shell off Beaufort, N.C. (Eastward Cruise E-10-70, Station 14452, a t 34"17' N and 76O7.7' W, May 1970, Courtesy Dr B. Coull). Sediment analysis with standard sieve series: 4.0 mm-0.480,!, 2 4 mm=2.08%, 1-2 mm=8.74%, 0.5-1 mm = 29.62 %, 0.25-0.5 mm = 51.21 %, 0.125-0.25 mm= 6.74 %, 0.063-0.025 mm=0.46%, 0.037-0.063 mm=0.1304,, silt-0.037 mm=0.07%, silt=0.27%,, clay-0.57%.